Arab states that have isolated Qatar tightened their squeeze on Friday by putting dozens of figures with links to the country on terrorism blacklists, while Qatar’s ally Turkey rushed to its side with plans to send troops, warships and planes.

The developments intensified a confrontation between tiny-but-wealthy Qatar and a group of Arab nations led by Saudi Arabia and Egypt that accuse it of fomenting instability. The dispute has created a major diplomatic test for the United States, which is a close ally of the countries on both sides.

In an apparent escalation of the crisis, staff at Al Jazeera, Qatar’s influential satellite television news channel which often infuriates the rulers of the Arab world, said its computer systems had come under cyberattack.

Riyadh, Cairo and their allies accuse Qatar, the world’s richest country per capita, of supporting militant Islamist movements across the region. They have imposed what Qatar says is a blockade of shipping and air traffic, and closed Qatar’s only land border, causing panic buying at supermarkets and

provoking confusion and anxiety across the population.

Qatar, which has developed an assertive foreign policy over the past decade, denies that it supports militants and says it is helping to reduce the threat of terrorism by backing groups that fight poverty and seek political reform.

Foreign Minister Sheikh Mohammed bin Abdulrahman Al Thani called the moves by Arab neighbors and others “clear violations of international law and international humanitarian law.

“They will not have a positive impact on the region but a negative one,” the minister said during a visit to Germany.

Qatar has vowed to ride out the isolation imposed on it by fellow Arab states and said it would not compromise its sovereignty over foreign policy to resolve the region’s biggest diplomatic crisis in years.

“The hour of diplomacy”

Qatar is home to 2.3 million people but only about 300,000 citizens: most of its population is comprised of foreign workers that helped to build the tiny finger off the Arabian Peninsula into a natural gas exporting powerhouse, crowned with skyscrapers. Other projects include soccer stadiums for the 2022 World Cup.

Armed Qatari gunboats patrolled the corniche of the capital Doha on Friday. A picture on Facebook showed a supermarket displaying food from Turkey including milk, eggs and chicken.

Tiny Qatar has played an outsized role as a sponsor of factions in wars and revolutions across the Middle East under its 37-year-old ruler, Tamim bin Hamad Al Thani, and his father Hamad who stepped down in 2013 after 18 years in power.

German Foreign Minister Sigmar Gabriel called for diplomatic efforts to resolve the crisis. “We are convinced that now is the hour of diplomacy and we must talk to each other; along with our American colleagues but above all our colleagues in the region, we must try to find solutions, especially lifting the sea and air blockades.”

Washington relies closely on the countries on both sides of the dispute for its military operations in the Gulf: Qatar hosts the U.S. Air Force’s biggest base in the region, while Bahrain hosts the U.S. Navy. Both Saudi Arabia and Qatar have funded rebels fighting in the Syrian civil war.

The confrontation erupted just weeks after U.S. President Donald Trump visited Saudi Arabia. Trump initially responded by tweeting his support for moves against Qatar, even as his State Department and Defense Department sought to remain neutral.

With supply chains disrupted and concern mounting about economic turbulence, banks and firms in Gulf Arab states were trying to keep business links to Qatar open and avoid a costly firesale of assets. The riyal currency has tumbled and the cost of insuring Qatari debt against default has risen.

Clashing over Brotherhood

Saudi Arabia, the United Arab Emirates (UAE), Egypt and Bahrain added 59 people to terrorist blacklists, among them 18 Qataris, including Abdullah bin Khalid Al Thani, a former interior minister and member of Qatar’s royal family.

The Qatari government said the move “reinforces baseless allegations that hold no foundation in fact.”

“Our position on countering terrorism is stronger than many of the signatories of the joint statement � a fact that has been conveniently ignored by the authors,” it said in a statement. Those on the list, including the former interior minister, could not be reached for comment.

Many of the others added to the list are figures associated with the Muslim Brotherhood who have made Qatar a base, including Brotherhood spiritual leader Yousef al-Qaradawi. Some are prominent jihadists who have fought in Libya and Syria.

Qatar has angered its neighbors for years by supporting the Brotherhood, a decades-old movement that calls for rule based on Islamic principles.

The Brotherhood says it eschews violence but some Arab states call it a terrorist movement. It was voted into power in Egypt in 2012 but toppled a year later by the military.

Turkish Warplanes and warships

Turkish President Tayyip Erdogan, whose AK Party has its roots in Islamist politics and who has voiced support for the Brotherhood, signaled his firm backing for Qatar by swiftly signing a law to send Turkish troops to a base there.

Showing how urgently Turkey is treating the matter, parliament passed the law on Wednesday, Erdogan signed it on Thursday and it was published in the state gazette by Friday.

Turkey will send warplanes and warships to Qatar after an initial deployment of troops to a Turkish base there, the mass-circulation Hurriyet newspaper said on its website.

“The number of Turkish warplanes and Turkish warships going to the base will become clear after the preparation of a report based on an initial assessment at the base,” Hurriyet said. Around 90 Turkish soldiers are currently at the base, it said.

Turkish officials were not immediately available to comment on the report but Hurriyet said there were plans to send some 200-250 soldiers within two months in the initial stage.

Staff at Al Jazeera said on Friday that a cyberattack had been dealt with at the Qatari state-funded network, watched by millions of people across the Arabic-speaking world.

“It is under control. We have one of the best teams available for countering cyberattacks. There have been repeated hacking attempts for the last two weeks on Al Jazeera’s platforms and yesterday those attempts intensified

Qatar also said last month its state news agency had been hacked and false statements attributed to the country’s ruler posted, helping ignite the current rift with other Arab states.

Saudi Arabia, Egypt, the UAE and Bahrain severed relations with Qatar on Monday, accusing it of supporting both Sunni Muslim Islamist militants and Shi’ite Muslim Iran — charges Qatar rejects. Several other countries later followed suit.

Would-be mediators, including Trump and Kuwait’s ruling emir, have struggled to ease the crisis. Trump initially tweeted his support for the Saudi-led group before apparently being nudged into a more even-handed approach when U.S. defense officials renewed praise of Qatar, home of the

al-Udeid base where the U.S. military commands its air missions across the Middle East and Afghanistan.

Qatar’s ambassador to Washington said on Thursday his government trusted Trump’s ability to resolve the dispute.

“The most important engagement that happened so far from the U.S. is by the president, which we highly appreciate,” Meshal bin Hamad al-Thani told the Financial Times. “We truly believe that the involvement of the president and the U.S. will bring this crisis to an end.”

The ambassador left open the prospect of compromise, saying: “We are courageous enough to acknowledge if things need to be amended.”